The present invention relates to thermoplastic compositions based on grafted rubber and polyester, a process for their manufacture, and industrial articles obtained from the compositions.
Examples in published European Patent Application No. 0,056,123 describe the preparation of a thermoplastic mass comprising 90% by weight of polybutylene terephthalate (PBTP) and 10% by weight of a grafted rubber, by mixing in an extruder at 250.degree. C. the PBTP and a grafted rubber produced in an aqueous dispersion and containing 35% by weight of water.
A slightly modified impact-polystyrene comprising:
from 20 to 80% by weight of a vinylaromatic polymer modified by the presence of 5 to 15% by weight of an unsaturated nitrile and, where applicable, a rubber, and PA1 from 20 to 80% by weight of a crystalline polyester having a molecular weight of preferably 10,000 to 60,000 PA1 the crystalline polyester is polybutylene terephthalate, and PA1 the polymer based on a vinylaromatic monomer, nitrile, and rubber is a specific polymer according to the present invention, different from the polymers used in the prior art. PA1 The vinylaromatic monomer (a) and the vinylaromatic monomer (e), which are identical or different from each other, are preferably chosen from styrene and its derivatives such as alpha-methylstyrene, vinyltoluene and vinylnaphthalene, PA1 the unsaturated nitrile (b) and the unsaturated nitrile (d), which are identical or different from each other, are preferably acrylonitrile, PA1 the rubber (c) is preferably chosen from polybutadiene, polyisoprene, butadiene/isoprene copolymers, and ethylene-propylene and ethylene-propylene-diene elastomers, PA1 the weight average molecular weight or the polybutylene terephthalate is preferably between 15,000 and 150,000. PA1 ethylene/vinyl acetate copolymers comprising from 30 to 80% by weight of acetate and from 20 to 70% by weight of ethylene, these copolymers being generally produced by emulsion polymerization, PA1 butadiene/acrylonitrile copolymers comprising, for example, from 60 to 85% by weight of butadiene and from 15 to 40% by weight of acrylonitrile, PA1 acrylic elastomers such as, in particular, styrene/butyl acrylate/methyl methacrylate copolymers and styrene/butadiene/methyl methacrylate copolymers, PA1 copolymers of a saturated polyester and a polyester, such as, in particular, the block copolymers of poly(butylene terephthalate) and of poly(tetramethylene glycol). PA1 the carboxylic acid salts of a metal chosen from the elements of groups IA, IIA, and IIB of the Periodic Classification, especially calcium, zinc, lithium, and magnesium stearates, PA1 oxidized polyethylene waxes, PA1 fatty acid esters such as glycerine, PA1 N,N'-ethylenebis(stearamide). PA1 an improved Izod impact strength (measured according to the ISO Standard R-180, equivalent to ASTM D 256), PA1 a higher Vicat temperature (measured according to the ISO Standard R-306, equivalent to ASTM D 1525), PA1 an improved multiaxial impact strength (measured according to the DIN standard 53 443), PA1 a higher hot flow index (measured according to the method described in the examples below).
is known from British Patent No. 2,118,194.
More precisely, Example 6 of this document describes a mixture of 75% by weight of a modified polystyrene (consisting of 84% by weight of styrene, 8% by weight of acrylonitrile and 8% by weight of rubber) and of 25% by weight of polybutylene terephthalate. This mixture has an Izod impact resistance of 49 J/m, considerably lower than that of the initial modified polystyrene.
Furthermore, French Patent No. 2,154,800, and especially its Example 20, discloses a mixture of 20% by weight of high molecular weight polybutylene terephthalate, 60% by weight of a terpolymer of acrylonitrile, butadiene and styrene, and 20% by weight of glass fiber reinforcement. This mixture has an Izod impact resistance of 65 J/m, well below that of a similar binary mixture in which the polybutylene terephthalate is replaced by the terpolymer of acrylonitride, butadiene, and styrene.
Thus, according to the teaching of the prior art, the introduction of 20 to 25% by weight of a high molecular weight crystalline polyester into a polymer based on styrene, acrylonitrile, and rubber results in a decrease in the impact strength of the composition, whether the latter is filled or not.